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Showing 1 to 20 of 57 for “"40Ar/39Ar"”.
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40Ar/39Ar, AFT and (U-Th)/He thermochronologic implications for the low-temperature geological evolution in SE Sweden
… thermal evolution, from c. 500 °C to c. 50 °C. 40Ar-39Ar geochronology on hornblende, muscovite and biotite, was applied to determine cooling from c. 500 °C to c. 300 °C, whereas apatite fission-track (AFT) and (U-Th)/He thermochronology were used to determine the thermal evolution between c. …
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The Role of Magmatism in the Catalina Metamorphic Core Complex, Arizona: Insights from Integrated Thermochronology, Gravity and Aeromagnetic Data
… evidence of zircon growth at <40 Ma.</p> <p>40Ar/39Ar data from the Wilderness suite sills indicate that the majority of the older 40Ar/39Ar apparent ages from both potassium feldspar and mica were obtained from the structurally higher sills in the main range, and the younger 40Ar/39Ar …
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Dynamic topography of the western Great Plains : geomorphic and 40Ar/39Ar evidence for mantle-driven uplift associated with the Jemez lineament, New Mexico and SE Colorado
… canyons and inverted, basalt-capped mesas. 40Ar/39Ar ages are used to define an episodic eruption history in the Raton-Clayton volcanic field and to quantify denudation rates from flow-capped paleosurfaces. Several datasets indicate patterns of surface topography that are consistent with …
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The use of detrital mineral thermochronology to explore relationships among climate, erosion, and tectonics in the Nepal Himalaya
… are evaluated using statistical comparisons of 40Ar/39Ar ages from Nepal and catchment area-elevation distributions. Bedrock 40Ar/39Ar data indicate that erosion rate estimates from detrital thermochronology yield the same rate as the traditional approach of analyzing bedrock cooling ages over a …
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High-Resolution Correlation of a Time-Bounded Unit of the Pisco Formation, Peru
… an interval bounded by two time markers, an 40Ar/39Ar-dated white tuff at the base and an 40Ar/39Ar-dated tuff couplet at the top. This interval was chosen because of the continuity and excellent exposure of the tuff beds at six distinct locations in a linear transect 30 km long. Correlation …
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Antarctica's Geologic and Ice Sheet History from Isotopic Sedimentary Provenance Studies
… fraction and employed isotopic measurements - 40Ar/39Ar on detrital hornblende and biotite grains, U-Pb on detrital zircons. I have also employed Nd isotope measurements on the terrigenous fine (< 63µm) fractions of these same samples. Chapter 2 is published in the journal Paleoceanography, and …
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⁴⁰Ar/³⁹Ar and U-Pb geochronological constraints on the thermal and tectonic evolution of the Connemara Caledonides, Western Ireland
… apparent ages using higher resolution U-Pb and 40Ar/ 39Ar geochronometers. The results indicate that arc magmatism, sillimanite-grade metamorphism, anatexis, and late fluid infiltration spanned only about 12 million years. Cooling following the metamorphic peak was actually relatively rapid at …
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Evolution of the Kingman Arch, southern Nevada
… Extensional Corridor. Apatite fission track and 40Ar/39Ar thermochronological analyses were conducted for granite samples collected from a 4.5 kilometer thick Precambrian section in the central McCullough Range. 40Ar/ 39Ar data suggest slow cooling of the Kingman Arch between 1000 to about 560 …
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Mesoproterozoic tectonic evolution of southwestern North America : protracted intracratonic deformation, sedimentation, and differential exhumation in Grand Canyon and the Rocky Mountain Region
… date the onset of deposition at ca. 1254 Ma. 40Ar/39Ar Kfeldspar thermochronology in Grand Canyon indicates that basement rocks cooled through 150˚ C between about 1300 and 1250 Ma, refining exhumation rates of basement rocks just prior to Unkar deposition. Abrupt thickness and facies changes …
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Tectonic and climatic controls on orogenic processes : the Northwest Himalaya, India
… orogen. Along the southern Himalayan front new 40Ar/39Ar white mica and apatite fission track (AFT) thermochronologic data provide the opportunity to determine the history of rock-uplift and exhumation paths along an approximately 120-km-wide NE-SW transect spanning the greater Sutlej region of …
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A Second North American Hot-spot: Pleistocene Volcanism in the Anahim Volcanic Belt, west-central British Columbia
… I report new whole-rock geochemical data and 40Ar/39Ar age determinations for two previously little-studied cone fields around Satah Mountain and Baldface Mountain in the central part of the AVB. Individual volcanic centres in these fields are generally small in extent and volume and most have …
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Kinematics and timing of normal faulting in a metamorphic core complex: Grouse Creek Mountains, Utah
… Utah, in the central Grouse Creek Mountains. 40Ar/39Ar thermochronology and kinematic studies indicate two periods of motion along the MMSZ in Eocene and Late Oligocene to Early Miocene time and motion along the sub-parallel Upper detachment in Middle Miocene time. Eocene fabrics record …
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Thermochronology and geobarometry of the Granite Mountains, southeast California: Exhumation of a plutonic complex during collapse of the Sevier orogen
… extensional tectonics. U/Pb zircon and 40Ar/39Ar ornblende ages indicate intrusion, crystallization, and geologically instantaneous cooling through 500°C at ∼75 Ma. K-feldspar multi-diffusion domain modeling indicates a cooling rate gradient from SW to NE of 63, 32, and 16°C/Ma for …
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Tectonic evolution of the Thakkahola Graben and Dhaulagiri Himalaya, Central Nepal
… Thakkhola graben, neotectonic, structural, and 40Ar/39Ar and U-Pb geochronologic data from the UMM record its Late Miocene to Quaternary exhumational history and reveal a kinematic and geometric relationship between core-complex extension in the UMM and rift extension in the Thakkhola graben.
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Understanding Non-Plume Related Intraplate Volcanism
… This study presents the first high precision 40Ar/39Ar ages along with new geochemical data, and radiogenic isotopes that constrain the melting conditions and the timing of emplacement. Modeling of the melting conditions suggests that melting occurred under conditions slightly higher than …
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Testing models of ultra-fast India-Asia convergence : new paleomagnetic results from Ladakh, Western Himalaya
… unit (Bhutani 2009, Dunlap 2002) have measured 40Ar-39Ar and U-Pb dates of -52-67 Ma. Assuming these ages apply to our samples, our results support the two-stage collision model of Jagoutz and Royden (in prep), which indicates an approximately equatorial India-KLA collision at 50 Ma.
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STRUCTURAL, THERMOCHRONOLOGICAL, AND STRATIGRAPHIC CONSTRAINTS ON THE EVOLUTION OF THE CLEARWATER METAMORPHIC CORE COMPLEX, IDAHO
… (SRFZ) was mapped. These faults yield footwall 40Ar/39Ar mica cooling ages of 44 Ma; the easternmost of these faults, the Surveyors fault, yields a hanging wall muscovite cooling age of 78 Ma, and thus delineates the eastern boundary of the CMCC. Faults of the SRFZ were crosscut after 44 Ma by …
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STRUCTURAL, THERMOCHRONOLOGICAL, AND STRATIGRAPHIC CONSTRAINTS ON THE EVOLUTION OF THE CLEARWATER METAMORPHIC CORE COMPLEX, IDAHO
… (SRFZ) was mapped. These faults yield footwall 40Ar/39Ar mica cooling ages of 44 Ma; the easternmost of these faults, the Surveyors fault, yields a hanging wall muscovite cooling age of 78 Ma, and thus delineates the eastern boundary of the CMCC. Faults of the SRFZ were crosscut after 44 Ma by …
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